Arduino Thermometer with... TV Output

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Analog video is getting replaced by digital signals which provide better resolution and picture without noise or interference. Although receivers for digital signals are cheap and popular, devices for generating such signals are expensive and intended for professional use only. On the other hand, analog video is easy to generate with simple hardware. You can even broadcast it over RF (on wire, not on air) with common modulators (standalone devices or modules from video game consoles, set top boxes, VCRs etc.).

An easy way to generate video signal is by using a microcontroller and some resistors. I'll use for this purpose an Arduino board (ATmega 328p) with the TVout library. The video signal is of low resolution and black&white. But it can be used to display data on a TV screen. If you no longer own a TV with analog video input, an USB capture card can be used. TVout library is interrupt based, therefore will interfere with some of other interrupt dependent microcontroller features.

Thermometer with TV Output
Thermometer with TV Output

Compute Heat Index with Arduino and DHT Sensor

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The heat index is a parameter that takes into account temperature and relative humidity, to determine the apparent temperature or the human perceived equivalent temperature. Heat index was developed in 1978 by George Winterling and was adopted next year. It is also known as humiture, according to Wikipedia contributors.

To compute this index, you need to know current temperature and relative humidity. An easy way to find both is by using an Arduino development board with a DHT sensor (DHT11, DHT22). These sensors measure temperature and humidity and send it to the microcontroller using a digital protocol. Thus, there is no need for calibration. You can read the values directly from the sensor module.

However, you should take into account that the accuracy of these sensors is not the best. DHT11 has an accuracy of +/-5% for humidity and +/-2 degrees Celsius for temperature. DHT22 (AM2302) is slightly better with an accuracy of +/-2% for humidity and +/-0.5 degrees Celsius for temperature. More than that, DHT22 has extended ranges for both temperature and humidity.

Compute Heat Index with Arduino and DHT Sensor

Audio Amplifier with Common Transistors

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Here is the schematic of a small audio amplifier that can provide up to 300mW to an 8 ohm load and can be used in low power devices like battery powered radios. This circuit can be an alternative to the LM386 IC. Due to the simplicity of the schematic, the circuit can be built also on breadboard, for those of you who want to experiment and learn how an amplifier works.

The design is straightforward. A common small signal NPN transistor (like BC547, 2N2222, 2N3904, S8050) drives a balanced power amplifier made of similar transistors. The output transistor pairs can be BC327 with BC337 or S8050 with S8550. They must handle peak currents of 300-400mA (this is why BC547/BC557 or 2N3904/2N3906 should not be used here).

The amplifier can be powered from a 9V battery or from a 12V power source. The circuit draws a current of about 170mA. The quiescent current is less than 10mA.

Audio amplifier with common transistors build on breadboard
Audio amplifier build on breadboard